Having a high conductivity, conductive polymers have been used as an electrolyte in aluminum electrolyte capacitors, tantalum electrolyte capacitors, niobium electrolyte capacitors, and etc.
The conductive polymers used in such an application can be obtained by means of chemical oxidation polymerization or electrolytic oxidation polymerization of, for example, thiophene or its derivatives.
As a dopant, an organic sulfonic acid can be mainly used to carry out a chemical oxidation polymerization of thiophene or its derivative as mentioned above. As an oxidant, a transition metal can be used. In particular, it is said that a ferric compound is suitable. Usually, a ferric salt of an organic sulfonic acid can be used to serve as an oxidant dopant agent in carrying out the chemical oxidation polymerization of thiophene or its derivative. (Patent Reference No. 1 and Patent Reference No. 2.)
However, in case of using ferric salts of organic sulfonic acids as an oxidant dopant agent to prepare a conductive polymer, thereby obtained electrolyte capacitors using it have been involved in large amounts of leak current. In particular, such problem of large amounts of leak current could become significant especially in a condition of a high temperature.